Challenges in the Design and Manufacture of Small Replacement Runners

The increasing trend within the hydro industry to achieve additional capacity and/or energy through runner replacement has brought with it new challenges for the turbine manufacturer. No longer are designers of runners able to start with a clean sheet of paper, nor do the manufacturing personnel have the liberty of generous schedules dictated by other concurrent plant construction operations. In addition, where the trend in conventional hydro development over the years has been toward ever larger units in terms of both capacity and physical size, the majority of the units currently being upgraded are those which were installed in the early part of this century. These units are relatively small and not well suited to the large facilities built to produce 'giant' turbines. This paper will describe some of these challenges associated with the replacement of small turbine runners and what one manufacturer is doing to meet them. It will look at the design criteria involved in maximizing capacity and/or energy within existing plant confines, new manufacturing technology that has been developed to meet the demands of ever shorter delivery requirements, and the manufacturing facilities installed by this manufacturer to support this current demand. Case studies of several recent runner replacement projects will be presented to show a variety of challenges and solutions.